Photodynamic therapy is a drug and device treatment using a photosensitizer, such as porfimer sodium, and red light energy at 630 nm to induce tumor destruction. In gastroenterology, PDT is approved for use in patients with esophageal cancer and Barrett's esophagus with high-grade dysplasia (a pre-cancerous condition). One of the principle challenges in the clinical utility of PDT is controlling treatment variables that affect the ability to deliver the uniform, precise delivery of light doses needed to produce the desired depth of injury with minimal damage to the surrounding normal tissues. PDT light dosing is critically important to clinical success since too little light will not effectively destroy the cancerous mucosal epithelium while too much light will lead to scarring, impaired esophageal motility, stricture and possible perforation. The long-term goal of this collaborative effort between physicians at Mayo Clinic and physicists at the College of Charleston is to improve light dosimetry for clinical esophageal photodynamic therapy (PDT). Our hypothesis is that such improvement in PDT light dosimetry will reduce the numbers of PDT treatment failures ("under dosing") and PDT associated strictures ("over dosing"). This study will involve collecting spectroscopic and clinical data, as well as biopsy specimens from the esophagus of a selected group of patients undergoing routine photodynamic therapy for Barrett's esophagus (BE) with high-grade dysplasia or for invasive esophageal cancer at the Mayo Clinic in Jacksonville, Florida (Herbert Wolfsen, MD and Michael Wallace, MD). The acquired data will be used by the Department of Physics at the College of Charleston (Linda Jones, PhD and Norris Preyer, Jr, PhD) for developing a computational model for optimal light dosimetry. With this model we aim to determine the depth of the lesion that is expected to receive a threshold light dose. Results of the computational model will be compared with clinical outcomes. The long-term goal of this collaborative effort is to improve light dosimetry for clinical esophageal photodynamic therapy. The results of this project will be used clinically in order to assess the ability of light modeling to improve clinical photodynamic therapy outcomes by the prevention of under treatment of cancer and dysplasia as well as avoiding over treatment and mucosal stricture. As esophageal photodynamic therapy is improved, it is likely to be used more often as an alternative to esophagectomy. [unreadable] [unreadable] [unreadable]